Comparative Morphology of Dendritic Spines and Spine Synapses

The following three-dimensional reconstructions are not a complete list of possible
spine and synapse variations. They only illustrate the most typical examples.

Hippocampus, rat

Fig. 1: A segment of pyramidal cell dendrite from stratum radiatum (CA1) with thin,
stubby, and mushroom-shaped spines. Spine synapses colored in red,
stem (or shaft) synapses colored in blue.
The dendrite was made transparent in the lower image to enable visualization of all synapses.

Fig. 2: Macular (left) and perforated (middle,right) spine synapses.
Macular synapses are typically located on stubby and thin spines, while perforated
synpases are usually found on mushroom spines.

Neocortex, human

Fig. 3: Human neocortical (frontal cortex) macular and perforated spine synapses.
Dendritic spines and synapses of neocortical pyramidal cells in humans have the
same appearance as those of laboratory animals.

Cerebellar cortex, mouse

Fig. 4: Numerous club-shaped spines on a dendritic branchlet of the
Purkinje cell in cerebellar cortex of mouse.

Fig. 5: Only macular synapses are located on Purkinje cell dendritic spines.

Fig. 6: Purkinje cell dendritic spines are rich in smooth endoplasmic
reticulum which is, however, lacking the higher differentiation (known as the spine apparatus)
found in mushroom spines of hippocampus and neocortex.

Thalamus, rat

Fig. 7: Complex spines in the thalamic ventrobasal nucleus.
They are associated with so called synaptic glomeruli.
The synaptic glomeruli are formed in this nucleus by lemniscal giant axon terminals
invaginated by ramified spines originating from proximal dendrites of thalamocortical relay neurons.

Fig. 8: Up to several macular synapses are present on one spine and several
tens of synapses are present in one glomerule.

Although most spines are located on dendrites,
spines are occasionally found on the neuron soma or on axonal initial segments.
These spines also receive synapses.